This invention relates to medical diagnostic instruments and more particularly to a retinoscope having a linear light polarizer filter mechanism for eliminating glare when refracting a patient's eye.
Prior art retinoscopes have heretofore not been equipped with filters for reducing glare. Retinoscopes are used in association with refractors or phoroptors in which a series of trial lenses are placed in the optical path of the instrument to determine a patient's refractive error. These trial lens devices contain a number of different specular lens surfaces as well as sealing windows, all of which can cause glare. Polarized light reflected from specular surfaces such as trial lenses, refractor windows and the cornea of the eye will remain polarized, while light reflected from a diffuse surface, such as the retina of the eye, will lose its polarization. By taking advantage of this phenomena, the glare reflected from specular surfaces in the optical path of a retinoscope can be virtually eliminated by placing a suitable polarization filter in the optical path of the instrument. The term optical path as herein used is broad enough to include both the viewing axis of the instrument and the light path of the instrument which typically are brought together by means of a beam splitter or the like.
Various prior art devices have offered different polarizing filters for the transmitted light and for the viewing light and they have been positioned in place by various levers and knobs. In U.S. Pat. No. 4,998,818 to Kugler et al., which has been assigned to a common assignee together with the present application, there is shown a device for positioning a pair of polarizing filters in the transmission and viewing pathways of an ophthalmoscope by actuation of a single control. This device has proven to be very effective and offers, in addition to the simplified insertion of the polarizing feature, other filter features all actuated by the same control.
The present invention is directed primarily to a retinoscope and provides a simplified single control apparatus for inserting and removing a polarizing filter system into the optical path of the instrument to reduce glare from specular surfaces in the optical path.